1. Field of the Invention
The invention relates to a liquid-cooled lance for blowing oxygen onto a steel bath.
2. Description of the Prior Art
Oxygen lances are in general use in the steel industry for the refining of steel in furnaces of the L.D. converter type. Oxygen under high pressure is blown onto the bath, with carbon and possibly other undesired elements in the steel being burned at the so-called burning spot thus created. The carbon is converted into a mixture of CO and CO.sub.2 and these gaseous products are removed through a flue above the converter. Some other combustion products from this reaction are taken into a layer of slag on the liquid steel surface and some leave as gaseous products through the flue. Such lances normally have a central duct for the oxygen surrounded by a double sleeve forming annular ducts for the supply and removal of cooling liquid.
In steel refining, the starting materials are often a mixture of liquid pig iron and scrap. The quantity of scrap which can be added is dependent on, among other things, the temperature of the liquid pig iron and on the amount of heat developed in the converter during the conversion of carbon to CO and CO.sub.2 respectively. The more CO.sub.2 that is formed, the more heat is developed and the more the scrap component can be increased.
In some cases it can be an advantage to combine the steel refining process with an injection of gas through the bottom of the vessel into the liquid steel. For instance, a better stirring effect can be achieved thereby. Such processes can, however, lead to an increased cooling of the bath which reduces the amount of scrap which can be added.
Especially if the price of scrap is low, it is desirable that the steel manufacturing process should allow a large scrap component.
One way of effecting this is to provide a secondary supply of oxygen from the lance which is blown obliquely from the side of the lance to form an oxygen screen around the burning spot. CO gas being formed at the burning spot is given off, and encounters the oxygen screen where it is burnt to CO.sub.2. In this way extra heat is supplied to the bath by way of radiation and convection from this secondary burning.
Lances with a secondary oxygen supply system are known. U.K. Pat. No. 1,349,069 (corresponding to U.S. Pat. No. 3,730,505) shows a lance in which the secondary oxygen is supplied to a plurality of nozzles in the side of the lance by an annular duct disposed between annular cooling liquid supply and removal ducts. U.K. Pat. No. 934,112 and U.S. Pat. No. 3,488,044 both show an annular duct for the supply of secondary oxygen immediately surrounding the central duct for the primary oxygen supply. U.S. Pat. No. 3,488,044 also suggests, as an alternative structure, that there is no separate supply duct for the secondary oxygen but that the secondary oxygen nozzles should be supplied from the primary oxygen supply duct.